netdev - Re: [PATCH 5/5] tun: vringfd xmit support.

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Message-Id: <200804200041.43969.rusty@rustcorp.com.au>
Date:	Sun, 20 Apr 2008 00:41:43 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	netdev@...r.kernel.org, Max Krasnyansky <maxk@...lcomm.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] tun: vringfd xmit support.

On Saturday 19 April 2008 05:06:34 Andrew Morton wrote:
> On Sat, 19 Apr 2008 01:15:15 +1000 Rusty Russell <rusty@...tcorp.com.au> 
wrote:
> > > What is the maximum numbet of pages which an unpriviliged user can
> > > concurrently pin with this code?
> >
> > Since only root can open the tun device, it's currently OK.  The old code
> > kmalloced and copied: is there some mm-fu reason why pinning userspace
> > memory is worse?
>
> We generally try to avoid it - it allows users to dos the box.

My question is: is pinning a page worse than allocating a (kernel) page in 
some way?

Cheers,
Rusty.
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